Korro Bio holder Atlas reports 5.9% stake

Atlas Venture funds filed Amendment No. 1 to Schedule 13D reporting their combined ownership in Korro Bio, Inc. common stock.

Rhea-AI Filing Summary

Atlas Venture funds filed Amendment No. 1 to Schedule 13D reporting their combined ownership in Korro Bio, Inc. common stock. Collectively, the reporting entities beneficially own 852,861 shares of common stock, representing an estimated 5.9% of Korro Bio’s outstanding shares.

Atlas Venture Fund XI, L.P. and its related general partners report 706,556 shares, or 4.9% of the outstanding common stock, with shared voting and dispositive power. Atlas Venture Opportunity Fund II, L.P. and its related general partners report 146,305 shares, or 1.0%. Percentages are based on 14,422,571 shares outstanding as of May 4, 2026. The funds are under common control and state they may be deemed a group, but they expressly disclaim group membership. Recent transactions within the past sixty days are listed in an exhibit.

Key Figures

Aggregate shares owned: 852,861 shares Aggregate ownership percentage: 5.9% Atlas Venture Fund XI shares: 706,556 shares +4 more

7 metrics

Aggregate shares owned 852,861 shares Aggregate shares of Korro Bio common stock beneficially owned by all Reporting Persons

Aggregate ownership percentage 5.9% Estimated percentage of Korro Bio outstanding common stock beneficially owned by all Reporting Persons

Atlas Venture Fund XI shares 706,556 shares Shares of common stock held by Atlas Venture Fund XI, L.P. with shared voting and dispositive power

Atlas Venture Fund XI ownership 4.9% Percentage of Korro Bio outstanding common stock attributable to the Fund XI Reporting Persons

Opportunity Fund II shares 146,305 shares Shares of common stock held by Atlas Venture Opportunity Fund II, L.P. with shared voting and dispositive power

Opportunity Fund II ownership 1.0% Percentage of Korro Bio outstanding common stock attributable to the Opportunity Fund II Reporting Persons

Shares outstanding 14,422,571 shares Korro Bio common stock outstanding as of May 4, 2026, per Form 10-Q

Key Terms

Schedule 13D, beneficially own, shared voting and dispositive power, Joint Filing Agreement, +1 more

5 terms

Schedule 13D regulatory

"This Amendment No. 1 to Schedule 13D relating to common stock"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

beneficially own financial

"may be deemed to beneficially own the shares held by Atlas XI"

Beneficially own means having the economic rights and risks of a security—such as the right to receive dividends, sell the shares, or profit from price changes—whether or not your name appears on the official share register. Think of it like renting a car: you use it and reap the benefits even if the title lists someone else. Investors care because beneficial ownership determines who truly controls value, must be disclosed under securities rules, and can signal potential influence or trading activity that affects a stock’s price.

shared voting and dispositive power financial

"Each has shared voting and dispositive power over the shares held"

Joint Filing Agreement regulatory

"99.1 Joint Filing Agreement (incorporated by reference)"

group membership regulatory

"Reporting Persons may be deemed to be members of a group"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What ownership stake do Atlas Venture funds report in Korro Bio (KRRO)?

Atlas Venture funds report beneficial ownership of 852,861 Korro Bio shares, representing an estimated 5.9% of the company’s outstanding common stock. This combines positions held by Atlas Venture Fund XI and Atlas Venture Opportunity Fund II and their related general partners.

How much of Korro Bio (KRRO) does Atlas Venture Fund XI own?

Atlas Venture Fund XI, L.P. reports owning 706,556 shares of Korro Bio common stock, equal to 4.9% of outstanding shares. Its general partners share voting and dispositive power over these shares and may be deemed to beneficially own them as well.

What is Atlas Venture Opportunity Fund II’s position in Korro Bio (KRRO)?

Atlas Venture Opportunity Fund II, L.P. reports beneficial ownership of 146,305 Korro Bio shares, representing 1.0% of the company’s outstanding common stock. Its associated general partners share voting and dispositive power over the shares held by this fund.

On what share count is Atlas Venture’s Korro Bio (KRRO) ownership percentage based?

The reported ownership percentages use a base of 14,422,571 Korro Bio common shares outstanding as of May 4, 2026. This outstanding share figure comes from Korro Bio’s Form 10-Q filed with the SEC on May 7, 2026.

Do the Atlas Venture reporting persons claim group status in Korro Bio (KRRO)?

The reporting persons note they are under common control and may be deemed a group, but they expressly disclaim group membership. They state that this Schedule 13D filing should not be viewed as an admission of group status under Section 13.

Does the filing describe recent trading in Korro Bio (KRRO) by Atlas Venture funds?

Yes. The filing states that transactions in Korro Bio common stock by the reporting persons within the past sixty days are detailed in Exhibit 99.2. Those trades are incorporated by reference rather than listed directly in the main disclosure text.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 08/04/2026 - 05:13 PM Accepted by SEC EDGAR 08/04/2026 - 05:13 PM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 1)

Korro Bio, Inc.

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

500946108

(CUSIP Number)

Ommer Chohan, CFO
Atlas Venture, 300 Technology Square, 8th Floor
Cambridge, MA, 02139
(857) 201-2700

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

06/24/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 500946108

1

Name of reporting person

Atlas Venture Fund XI, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 706,556.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 706,556.00

11

Aggregate amount beneficially owned by each reporting person

706,556.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

4.9 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP Number(s): 500946108

1

Name of reporting person

Atlas Venture Associates XI, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 706,556.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 706,556.00

11

Aggregate amount beneficially owned by each reporting person

706,556.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

4.9 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP Number(s): 500946108

1

Name of reporting person

Atlas Venture Associates XI, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 706,556.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 706,556.00

11

Aggregate amount beneficially owned by each reporting person

706,556.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

4.9 %

14

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13D

CUSIP Number(s): 500946108

1

Name of reporting person

Atlas Venture Opportunity Fund II, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 146,305.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 146,305.00

11

Aggregate amount beneficially owned by each reporting person

146,305.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

1.0 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP Number(s): 500946108

1

Name of reporting person

Atlas Venture Associates Opportunity II, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 146,305.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 146,305.00

11

Aggregate amount beneficially owned by each reporting person

146,305.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

1.0 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP Number(s): 500946108

1

Name of reporting person

Atlas Venture Associates Opportunity II, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 146,305.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 146,305.00

11

Aggregate amount beneficially owned by each reporting person

146,305.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

1.0 %

14

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.001 per share
(b)	Name of Issuer: Korro Bio, Inc.
(c)	Address of Issuer's Principal Executive Offices: 60 First Street, 2nd Floor, Suite 250, Cambridge, MASSACHUSETTS , 02141.
Item 1 Comment: This Amendment No. 1 to Schedule 13D ("Amendment No. 1") is being filed as an amendment to the statement on Schedule 13D relating to common stock, par value $0.001 per share of Korro Bio, Inc., a Delaware corporation, as filed with the Securities and Exchange Commission (the "SEC") on November 13, 2023 (the "Original Schedule 13D"). All capitalized terms not otherwise defined herein shall have the meanings ascribed to the terms in the Original Schedule 13D. The Original Schedule 13D is hereby amended and supplemented as follows and, except as expressly amended below, the Original Schedule 13D remains in full force and effect.
Item 5.	Interest in Securities of the Issuer
(a)	As of the date hereof, Atlas XI is the record owner of 706,556 shares of Common Stock. AVA XI LP is the general partner of Atlas XI and AVA XI LLC is the general partner of AVA XI LP. Each of Atlas XI, AVA XI LP and AVA XI LLC has shared voting and dispositive power over the shares held by Atlas XI. As such, each of Atlas XI, AVA XI LP and AVA XI LLC may be deemed to beneficially own the shares held by Atlas XI. As of the date hereof, AVOF II is the record owner of 146,305 shares of Common Stock. AVAO II LP is the general partner of AVOF II and AVAO II LLC is the general partner of AVAO II LP. Each of AVOF II, AVAO II LP and AVAO II LLC has shared voting and dispositive power over the shares held by AVOF II. As such, each of AVOF II, AVAO II LP and AVAO II LLC may be deemed to beneficially own the shares held by AVOF II. Each of the Fund XI Reporting Persons and the Opportunity Fund II Reporting Persons may be deemed to beneficially own 4.9% and 1.0%, respectively, of the Issuer's outstanding Common Stock, which percentages are calculated based upon 14,422,571 shares of Common Stock outstanding as of May 4, 2026, as reported in the Issuer's Form 10-Q filed with the Securities and Exchange Commission on May 7, 2026. Collectively, the Reporting Persons beneficially own an aggregate of 852,861 shares of Common Stock, which represents an estimated 5.9% of the Issuer's outstanding Common Stock. The Fund XI Reporting Persons and the Opportunity Fund II Reporting Persons are under common control and as a result, the Reporting Persons may be deemed to be members of a group. However, the Reporting Persons disclaim such group membership, and this Schedule 13D shall not be deemed an admission that the Reporting Persons are members of a group for purposes of Section 13 or for any other purposes.
(b)	Each of Atlas XI, AVA XI LP and AVA XI LLC has shared voting and dispositive power over 706,556 shares held by Atlas XI. Each of AVOF II, AVAO II LP and AVAO II LLC has shared voting and dispositive power over 146,305 shares held by AVOF II.
(c)	The transactions in the common stock by the Reporting Persons subsequent to the date that is sixty days prior to the date of the triggering of this filing are set forth in Exhibit 99.2 and are incorporated herein by reference.
(d)	No other person is known by the Reporting Persons to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the shares of Common Stock beneficially owned by the Reporting Persons.
(e)	Not applicable.
Item 7.	Material to be Filed as Exhibits.
	99.1 Joint Filing Agreement (incorporated by reference to Exhibit A to the Reporting Persons' Schedule 13D, filed with the SEC on November 13, 2023). 99.2 Transactions in Common Stock During the Past Sixty Days

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Atlas Venture Fund XI, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates XI, L.P., its general partner, By: Atlas Venture Associates XI, LLC, its general partner, By: Ommer Chohan, CFO
Date:	08/04/2026

Atlas Venture Associates XI, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates XI, LLC, its general partner, By: Ommer Chohan, CFO
Date:	08/04/2026

Atlas Venture Associates XI, LLC

Signature:	/s/ Ommer Chohan
Name/Title:	Ommer Chohan, CFO
Date:	08/04/2026

Atlas Venture Opportunity Fund II, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates Opportunity II, L.P., its GP, By: Atlas Venture Associates Opportunity II, LLC, its GP, By: Ommer Chohan, CFO
Date:	08/04/2026

Atlas Venture Associates Opportunity II, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates Opportunity II, LLC, its GP, By: Ommer Chohan, CFO
Date:	08/04/2026

Atlas Venture Associates Opportunity II, LLC

Signature:	/s/ Ommer Chohan
Name/Title:	By: Ommer Chohan, CFO
Date:	08/04/2026